Human RNA viruses are characterized by large genetic variation among isolates, rapid mutation rates and efficient adaptability to changing environments. The objective of this proposal and long-term goal of this research is to use fish rhabdoviruses as a model systems to better understand the mechanisms affecting the genetic variation and evolution of RNA viruses. Fish viruses offer a unique system to study because of the fish host., waterborne transmission, and lower temperature requirement for fish and in vivo fish may be more feasible than other vertebrates in terms of sample size and cost. The specific aims of this project are to: 1) Characterize the genetic diversity of a warm water fish rhabdovirus, spring viremia of carp (SVCV) isolates throughout its range (Eastern Europe) by conducting sequence analysis on variable regions within glycoprotein, matrix and polymerase genes. The results will determine if the genetic diversity of this virus follow the patterns found in previous studies involving infectious hematopoietic necrosis virus (IHNV) and viral hemorrhagic septicemia virus (VHSV), two cold water fish rhabdoviruses that have less genetic variation than mammalian rhabdoviruses or whether SVCV has grater genetic diversity perhaps because it is a warm water fish rhabdovirus. 2) Examine the effect of temperature (rate of virus replication and rate of base substitution) on the genetic diversity and evolution of SVCV. Genetic diversity and evolution will be measured by sequence analysis and measurements of fitness. Long-term it will be possible to compare the evolution of SVCV and IHNV in cell culture and in vivo systems and determine the influence of temperatures on genetic variation and evolution of fish rhabdoviruses. Once the cell and determine the influence of temperature on genetic variation and evolution of fish rhabdoviruses. Once the cell culture and fish model systems are established, studies examining other parameters affecting the evolution of fish rhabdoviruses can be done such as the impact of immune selection and the evolution of virulence. The significance of these experiments on human diseases will be to cast light on the population structure and evolution of a class of these experiments on human diseases will be to cast light on the population structure and evolution of a class of pathogen that have unique host and ecological characteristics that has not been investigated before in detail. The results can shed further light on the mechanisms effecting the diversity, evolution and virulence of RNA viruses.